Turbine oil comprising an ester component

ABSTRACT

Provided is a turbine oil formulation comprised of a base oil selected from the group consisting of Group II, III and IV base oils and mixtures thereof, and an ester component comprised of at least one diester or triester species having ester links on adjacent carbons. The formulation exhibits less than 6 mg of sludge/100 ml of turbine oil, and is imminently suitable for use as a turbine oil.

FIELD OF THE INVENTION

This invention relates to turbine oil compositions and their manufacture, and specifically to turbine oils comprised of an ester species having ester links on adjacent carbons. The use of such esters can provide biodegradable turbine oils having reduced sludge.

BACKGROUND

Esters have been used as lubricating oils for over 50 years. They are used in a variety of applications ranging from jet engines to refrigeration. In fact, esters were the first synthetic crankcase motor oils in automotive applications. However, esters have largely given way to polyalphaolefins (PAOs) due to the lower cost of PAOs and their formulation similarities to mineral oils. In fully synthetic motor oils, however, esters are almost always used in combination with PAOs to balance the effect on seals, additive solubility, volatility reduction, and energy efficiency improvement by enhanced lubricity.

Ester-based lubricants, in general, have excellent lubrication properties due to the polarity of the ester molecules of which they are comprised. Due to the polarity of the ester functionality, esters have a stronger affinity for metal surfaces than PAOs and mineral oils. As a result, they are very effective in establishing protective films on metal surfaces, such protective films serving to mitigate the wear of such metals. Such lubricants are less volatile than the traditional lubricants and tend to have much higher flash points and much lower vapor pressures. Ester lubricants are excellent solvents and dispersants, and can readily solvate and disperse the degradation by-products of oils, i.e., they greatly reduce sludge buildup. While ester lubricants are relatively stable to thermal and oxidative processes, the ester functionalities give microbes a handle with which to do their biodegrading more efficiently and more effectively than their mineral oil-based analogues—thereby rendering them more environmentally-friendly. However, as previously alluded to, the preparation of esters is more involved and more costly than that of their PAO counterparts.

Recently, novel diester-based lubricant compositions and their corresponding manufacture have been described in Miller et al., United States Patent Application Publication No. 20080194444 A1, published Aug. 14, 2008; and in Miller et al., United States Patent Publication No. 20090198075 A1, published Aug. 6, 2009. The diester syntheses described in these patent applications render the economics of diester lubricant formulations more favorable.

Increased usage of Group II (and higher) base oils in finished lubricants such as turbine oils has coincided with an increased awareness of insoluble formation in the finished lubricants. Such an increase in insolubles formation is particularly detrimental in turbine oils. Providing a turbine oil with good properties but less sludge build-up would be of great benefit to the industry.

SUMMARY

Provided is a turbine oil formulation comprised of a base oil selected from the group consisting of Group II, III and IV base oils and mixtures thereof, and an ester component comprised of at least one diester or triester species having ester links on adjacent carbons. The formulation exhibits less than 6 mg of sludge/100 ml of turbine oil as determined by the Cincinnati Milacron Thermal A test, and is imminently suitable for use as a turbine oil.

Among other factors, the present turbine oil formulation comprising the present diester and triester species having ester links on adjacent carbons, provides a turbine oil with a good balance of properties while also providing a biodegradable alternative. In particular, the turbine oil exhibits reduced sludge, and can also exhibit improved copper appearance and improved oxidation stability in RPVOT. The starting olefins and carboxylic acids used in preparing the diesters and triesters also provides an economical manufacturing route.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention is directed to a turbine oil composition having an ester component. The ester component is comprised of at least one diester or triester species having ester links on adjacent carbons, which ester component can also be bio-derived.

In some embodiments, bio-derived (i.e., derived from a renewable biomass source) fatty (carboxylic) acid moieties are reacted with Fischer-Tropsch (FT)/gas-to-liquids (GTL) reaction products and/or by-products (i.e., α-olefins) to yield bio-derived diester and triester species that can then be selectively blended with base stock (oil) and one or more additive species to yield a turbine oil finished lubricant product having a biomass-derived component.

Because biolubricants and biofuels are increasingly capturing the public's attention and becoming topics of focus for many in the oil industry, the use of biomass in the making of turbine oils could be attractive from several different perspectives (e.g., renewability, regulatory, economic, etc.). As biomass is utilized in the making of the present ester component of the turbine oil described herein, such a turbine oil is deemed to be a biolubricant—or at the very least, they are deemed to comprise a bio-derived component.

DEFINITIONS

“Lubricants,” as defined herein, are substances (usually a fluid under operating conditions) introduced between two moving surfaces so to reduce the friction and wear between them. This definition is intended to include greases, whose viscosity drops dramatically upon application of shear.

Herein, “base oil” will be understood to mean the single largest component (by weight) of a lubricant composition. Base oils are categorized into five groups (I-V) by the American Petroleum Institute (API). See API Publication Number 1509. The API Base Oil Category, as shown in the following table (Table 1), is used to define the compositional nature and/or origin of the base oil.

TABLE 1 Base Oil Category Sulfur (%) Saturates (%) Viscosity Index Group I >0.03 and/or <90 80 to 120 Group II <0.03 and >90 80 to 120 Group III <0.03 and >90 >120 Group IV All polyalphaolefins (PAOs) Group V All others not included in Groups I, II, III or IV (e.g., esters)

“Mineral base oils,” as defined herein, are those base oils produced by the refining of a crude oil.

“Centistoke,” abbreviated “cSt,” is a unit for kinematic viscosity of a fluid (e.g., a lubricant), wherein 1 centistoke equals 1 millimeter squared per second (1 cSt=1 mm²/s). See, e.g., ASTM Standard Guide and Test Method D 2270-04. Herein, the units cSt and mm²/s are used interchangeably.

With respect to describing molecules and/or molecular fragments herein, “R_(n),” where “n” is an index, refers to a hydrocarbon group, wherein the molecules and/or molecular fragments can be linear and/or branched.

As defined herein, “C_(n),” where “n” is an integer, describes a hydrocarbon molecule or fragment (e.g., an alkyl group) wherein “n” denotes the number of carbon atoms in the fragment or molecule.

The term “carbon number” is used herein in a manner analogous to that of “C_(n).” A difference, however, is that carbon number refers to the total number of carbon atoms in a molecule (or molecular fragment) regardless of whether or not it is purely hydrocarbon in nature. Linoleic acid, for example, has a carbon number of 18.

The term “internal olefin,” as used herein, refers to an olefin (i.e., an alkene) having a non-terminal carbon-carbon double bond (C═C). This is in contrast to “α-olefins” which do bear a terminal carbon-carbon double bond.

The term “vicinal,” as used herein, refers to the attachment of two functional groups (substituents) to adjacent carbons in a hydrocarbon-based molecule, e.g., vicinal diesters.

The term “fatty acid moiety,” as used herein, refers to any molecular species and/or molecular fragment comprising the acyl component of a fatty (carboxylic) acid.

The prefix “bio,” as used herein, refers to an association with a renewable resource of biological origin, such as resource generally being exclusive of fossil fuels. Such an association is typically that of derivation, i.e., a bio-ester derived from a biomass precursor material.

“Fischer-Tropsch products,” as defined herein, refer to molecular species derived from a catalytically-driven reaction between CO and H₂ (i.e., “syngas”). See, e.g., Dry, “The Fischer-Tropsch process: 1950-2000,” vol. 71(3-4), pp. 227-241, 2002; Schulz, “Short history and present trends of Fischer-Tropsch synthesis,” Applied Catalysis A, vol. 186, pp. 3-12, 1999; Claeys and Van Steen, “Fischer-Tropsch Technology,” Chapter 8, pp. 623-665, 2004.

“Gas-to-liquids,” as used herein, refers to Fischer-Tropsch processes for generating liquid hydrocarbons and hydrocarbon-based species (e.g., oxygenates).

The term “comprising” means including the elements or steps that are identified following that term, but any such elements or steps are not exhaustive, and an embodiment can include other elements or steps.

“Copper Appearance” refers to the copper corrosion caused by the turbine oil as determined by ASTM D130-10, “Standard Test Method for Corrosiveness to Copper from Petroleum Products by Copper Strip Test.” The lower the number and letter the less corrosion indicated.

“RPVOT” refers to the oxidation stability of the turbine oil itself, as determined by ASTM D2272-11, “Standard Test Method for Oxidation Stability of Steam Turbine Oils by Rotating Pressure Vessel.”

The ability of the turbine oil to prevent the rusting of ferrous parts should water become mixed with the oil is determined by ASTM D665-06, “Standard Test Method for Rust-Preventing Characteristics of Inhibited Mineral Oil in the Presence of Water.”

The test method for determining the relative changes that occur in an oil during use under oxidizing conditions is measured using ASTM D974-08, “Standard Test Method for Acid and Base Number by Color-Indicator Titration.”

The thermal stability of hydrocarbon based oils is determined by ASTM D2070-91, “Standard Test Method for Thermal Stability of Hydraulic Oils.”

Base Oils Used in the Turbine Oils

The present turbine oils comprise a base oil selected from the group consisting of Group II, III, IV base oils and mixtures thereof. The Group II, III and IV base oils are as understood and shown in Table 1, which include Gas-to-Liquid (GTL) derived based oils. In some embodiments, the base oils contain less than 10 wt %, and more likely less than 5 wt % aromatics. The base oil is then combined with a quantity of an ester component, which is either a diester or triester species, or a mixture thereof, which ester component species has ester links on adjacent carbons. The quantity of ester component is generally in the range of from 0.5 to 15 wt % based on the turbine oil formulation. In some embodiments, the quantity of ester component will range from 5 to 10 wt %. In one embodiment, an additive is also combined with the base oil and ester component. The additive can be added to the base oil first, the ester first, or upon combining all individual components. In some embodiments, the additive comprises an antioxidant composition comprised of at least one antioxidant other than a phenolic antioxidant.

Diester Component

In some embodiments, the ester component combined with the base oil comprises a diester species having the following chemical structure:

where R₁, R₂, R₃, and R₄ are the same or independently selected from a C₂ to C₁₇ carbon fragment.

Regarding the above-mentioned diester species, selection of R₁, R₂, R₃, and R₄ can follow any or all of several criteria. For example, in some embodiments, R₁, R₂, R₃, and R₄ are selected such that the kinematic viscosity of the composition at a temperature of 100° C. is typically 3 mm²/sec or greater. In some or other embodiments, R₁, R₂, R₃, and R₄ are selected such that the pour point of the resulting electrical insulating oil is −10° C. or lower, −25° C. or lower; or even −40° C. or lower. In some embodiments, R₁ and R₂ are selected to have a combined carbon number (i.e., total number of carbon atoms) of from 6 to 14. In these or other embodiments, R₃ and R₄ are selected to have a combined carbon number of from 10 to 34. Depending on the embodiment, such resulting diester species can have a molecular mass between 340 atomic mass units (a.m.u.) and 780 a.m.u.

In some embodiments, the ester component is substantially homogeneous in terms of its diester component. In some or other embodiments, the diester component comprises a variety (i.e., a mixture) of diester species.

In some embodiments, the diester component comprises at least one diester species derived from a C₈ to C₁₆ olefin and a C₂ to C₁₈ carboxylic acid. Typically, the diester species are made by reacting each —OH group (on the intermediate) with a different acid, but such diester species can also be made by reacting each —OH group with the same acid.

In some of the above-described embodiments, the diester component combined with the base oil to prepare the turbine oil comprises a diester species selected from the group consisting of decanoic acid 2-decanoyloxy-1-hexyl-octyl ester and its isomers, tetradecanoic acid-1-hexyl-2-tetradecanoyloxy-octyl esters and its isomers, dodecanoic acid 2-dodecanoyloxy-1-hexyl-octyl ester and its isomers, hexanoic acid 2-hexanoyloxy-1-hexy-octyl ester and its isomers, octanoic acid 2-octanoyloxy-1-hexyl-octyl ester and its isomers, hexanoic acid 2-hexanoyloxy-1-pentyl-heptyl ester and isomers, octanoic acid 2-octanoyloxy-1-pentyl-heptyl ester and isomers, decanoic acid 2-decanoyloxy-1-pentyl-heptyl ester and isomers, decanoic acid-2-cecanoyloxy-1-pentyl-heptyl ester and its isomers, dodecanoic acid-2-dodecanoyloxy-1-pentyl-heptyl ester and isomers, tetradecanoic acid 1-pentyl-2-tetradecanoyloxy-heptyl ester and isomers, tetradecanoic acid 1-butyl-2-tetradecanoyloxy-hexy ester and isomers, dodecanoic acid-1-butyl-2-dodecanoyloxy-hexyl ester and isomers, decanoic acid 1-butyl-2-decanoyloxy-hexyl ester and isomers, octanoic acid 1-butyl-2-octanoyloxy-hexyl ester and isomers, hexanoic acid 1-butyl-2-hexanoyloxy-hexyl ester and isomers, tetradecanoic acid 1-propyl-2-tetradecanoyloxy-pentyl ester and isomers, dodecanoic acid 2-dodecanoyloxy-1-propyl-pentyl ester and isomers, decanoic acid 2-decanoyloxy-1-propyl-pentyl ester and isomers, octanoic acid 1-2-octanoyloxy-1-propyl-pentyl ester and isomers, hexanoic acid 2-hexanoyloxy-1-propyl-pentyl ester and isomers, and mixtures thereof.

Methods of Making the Diester Components

Methods which can be employed in making the diesters are further described in U.S. Patent Application Publications 2009/0159837 and 2009/0198075, which publications are incorporated by reference herein in their entirety.

More specifically, in some embodiments, the processes for making the above-mentioned diester species, comprise the following steps: epoxidizing an olefin (or quantity of olefins) having a carbon number of from 8 to 16 to form an epoxide comprising an epoxide ring; opening the epoxide ring to form a diol; and esterifying (i.e., subjecting to esterification) the diol with an esterifying species to form a diester species, wherein such esterifying species are selected from the group consisting of carboxylic acids, acyl acids, acyl halides, acyl anhydrides, and combinations thereof; wherein such esterifying species have a carbon number from 2 to 18; and wherein the diester species have a viscosity of 3 mm²/sec or more at a temperature of 100° C.

Furthermore, the diester species can be prepared by epoxidizing an olefin having from about 8 to about 16 carbon atoms to form an epoxide comprising an epoxide ring. The epoxidized olefin is reacted directly with an esterifying species to form a diester species, wherein the esterifying species is selected from the group consisting of carboxylic acids, acyl halides, acyl anhydrides, and combinations thereof, wherein the esterifying species has a carbon number of from 2 to 18, and wherein the diester species has a viscosity and a pour point suitable for use as an electrical insulating oil.

In some embodiments, where a quantity of such diester species is formed, the quantity of diester species can be substantially homogeneous, or it can be a mixture of two or more different such diester species.

In some such above-described method embodiments, the olefin used is a reaction product of a Fischer-Tropsch process. In these or other embodiments, the carboxylic acid can be derived from alcohols generated by a Fischer-Tropsch process and/or it can be a bio-derived fatty acid.

In some embodiments, the olefin is an α-olefin (i.e., an olefin having a double bond at a chain terminus). In such embodiments, it is usually necessary to isomerize the olefin so as to internalize the double bond. Such isomerization is typically carried out catalytically using a catalyst such as, but not limited to, crystalline aluminosilicate and like materials and aluminophosphates. See, e.g., U.S. Pat. Nos. 2,537,283; 3,211,801; 3,270,085; 3,327,014; 3,304,343; 3,448,164; 4,593,146; 3,723,564 and 6,281,404; the last of which claims a crystalline aluminophosphate-based catalyst with 1-dimensional pores of size between 3.8 Å and 5 Å.

As an example of such above-described isomerizing, Fischer-Tropsch alpha olefins (α-olefins) can be isomerized to the corresponding internal olefins followed by epoxidation. The epoxides can then be transformed to the corresponding diols via epoxide ring opening followed by di-acylation (i.e., di-esterification) with the appropriate carboxylic acids or their acylating derivatives. It is typically necessary to convert alpha olefins to internal olefins because diesters of alpha olefins, especially short chain alpha olefins, tend to be solids or waxes. “Internalizing” alpha olefins followed by transformation to the diester functionalities introduces branching along the chain which reduces the pour point of the intended products. The ester groups with their polar character would further enhance the viscosity of the final product. Adding ester branches will increase the carbon number and hence viscosity. It can also decrease the associated pour and cloud points. It is typically preferable to have a few longer branches than many short branches, since increased branching tends to lower the viscosity index (VI).

Regarding the step of epoxidizing (i.e., the epoxidation step), in some embodiments, the above-described olefin (in one embodiment an internal olefin) can be reacted with a peroxide (e.g., H₂O₂) or a peroxy acid (e.g., peroxyacetic acid) to generate an epoxide. See, e.g., D. Swern, in Organic Peroxides Vol. II, Wiley-Interscience, New York, 1971, pp. 355-533; and B. Plesnicar, in Oxidation in Organic Chemistry, Part C, W. Trahanovsky (ed.), Academic Press, New York 1978, pp. 221-253. Olefins can be efficiently transformed to the corresponding diols by highly selective reagent such as osmium tetra-oxide (M. Schroder, Chem. Rev. vol. 80, p. 187, 1980) and potassium permanganate (Sheldon and Kochi, in Metal-Catalyzed Oxidation of Organic Compounds, pp. 162-171 and 294-296, Academic Press, New York, 1981).

Regarding the step of epoxide ring opening to the corresponding diol, this step can be acid-catalyzed or based-catalyzed hydrolysis. Exemplary acid catalysts include, but are not limited to, mineral-based Brønsted acids (e.g., HCl, H₂SO₄, H₃PO₄, perhalogenates, etc.), Lewis acids (e.g., TiCl₄ and AlCl₃) solid acids such as acidic aluminas and silicas or their mixtures, and the like. See, e.g., Chem. Rev. vol. 59, p. 737, 1959; and Angew. Chem. Int. Ed., vol. 31, p. 1179, 1992. Based-catalyzed hydrolysis typically involves the use of bases such as aqueous solutions of sodium or potassium hydroxide.

Regarding the step of esterifying (esterification), an acid is typically used to catalyze the reaction between the —OH groups of the diol and the carboxylic acid(s). Suitable acids include, but are not limited to, sulfuric acid (Munch-Peterson, Org. Synth., V, p. 762, 1973), sulfonic acid (Allen and Sprangler, Org. Synth., III, p. 203, 1955), hydrochloric acid (Eliel et al., Org. Synth., IV, p. 169, 1963), and phosphoric acid (among others). In some embodiments, the carboxylic acid used in this step is first converted to an acyl chloride (via, e.g., thionyl chloride or PCl₃). Alternatively, an acyl chloride could be employed directly. Wherein an acyl chloride is used, an acid catalyst is not needed and a base such as pyridine, 4-dimethylaminopyridine (DMAP) or triethylamine (TEA) is typically added to react with an HCl produced. When pyridine or DMAP is used, it is believed that these amines also act as a catalyst by forming a more reactive acylating intermediate. See, e.g., Fersh et al., J. Am. Chem. Soc., vol. 92, pp. 5432-5442, 1970; and Hofle et al., Angew. Chem. Int. Ed. Engl., vol. 17, p. 569, 1978.

Regardless of the source of the olefin, in some embodiments, the carboxylic acid used in the above-described method is derived from biomass. In some such embodiments, this involves the extraction of some oil (e.g., triglyceride) component from the biomass and hydrolysis of the triglycerides of which the oil component is comprised so as to form free carboxylic acids.

Triester Component

In some embodiments, the ester component combined with the base oil comprises a triester species having the following chemical structure:

wherein R₁, R₂, R₃, and R₄ are the same or independently selected from C₂ to C₂₀ hydrocarbon groups (groups with a carbon number from 2 to 20), and wherein “n” is an integer from 2 to 20.

Regarding the above-mentioned triester species, selection of R₁, R₂, R₃, and R₄, and n can follow any or all of several criteria. For example, in some embodiments, R₁, R₂, R₃, and R₄ and n are selected such that the kinematic viscosity of the composition at a temperature of 100° C. is typically 3 mm²/sec or greater. In some or other embodiments, R₁, R₂, R₃, and R₄ and n are selected such that the pour point of the resulting electrical insulating oil is −10° C. or lower, e.g., −25° C. or even −40° C. or lower. In some embodiments, R₁ is selected to have a total carbon number of from 6 to 12. In these or other embodiments, R₂ is selected to have a carbon number of from 1 to 20. In these or other embodiments, R₃ and R₄ are selected to have a combined carbon number of from 4 to 36. In these or other embodiments, n is selected to be an integer from 5 to 10. Depending on the embodiment, such resulting triester species can typically have a molecular mass between 400 atomic mass units (a.m.u.) and 1100 a.m.u., and more typically between 450 a.m.u. and 1000 a.m.u.

In some embodiments, the ester component is substantially homogeneous in terms of its triester component. In some other embodiments, the triester component comprises a variety (i.e., a mixture) of such triester species. In these or other embodiments, such above-described triester components further comprise one or more triester species.

In some of the above-described embodiments, the triester component combined with the base oil to prepare the turbine oil comprises one or more triester species of the type 9,10-bis-alkanoyloxy-oetadecanoic acid alkyl ester and isomers and mixtures thereof, where the alkyl is selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, and octadecyl; and where the alkanoyloxy is selected from the group consisting of ethanoyloxy, propanoyoxy, butanoyloxy, pentanoyloxy, hexanoyloxy, heptanoyloxy, octanoyloxy, nonaoyloxy, decanoyloxy, undacanoyloxy, dodecanoyloxy, tridecanoyloxy, tetradecanoyloxy, pentaclecanoyloxy, hexadeconoyloxy, and octadecanoyloxy, 9,10-bis-hexanoyloxy-octadecanoic acid hexyl ester and 9,10-bis-decanoyloxy-octadecanoic acid decyl ester are exemplary such triesters.

Methods of Making the Triester Component

One method of preparing the triester species is described in U.S. Pat. No. 7,544,645, which is incorporated herein by reference in its entirety.

More specifically, in some embodiments, processes for making the above-mentioned triester species comprises the following steps: esterifying (i.e., subjecting to esterification) a mono-unsaturated fatty acid (or quantity of mono-unsaturated fatty acids) having a carbon number of from 10 to 22 with an alcohol to form an unsaturated ester (or a quantity thereof); epoxidizing the unsaturated ester to form an epoxy-ester species comprising an epoxide ring; opening the epoxide ring of the epoxy-ester species to form a dihydroxy-ester: and esterifying the dihydroxy-ester with an esterifying species to form a triester species, wherein such esterifying species are selected from the group consisting of carboxylic acids, acyl halides, acyl anhydrides, and combinations thereof; and wherein such esterifying species have a carbon number of from 2 to 19.

In another embodiment, the method can comprise reducing a monosaturated fatty acid to the corresponding unsaturated alcohol. The unsaturated alcohol is then epoxidized to an epoxy fatty alcohol. The ring of the epoxy fatty alcohol is opened to make the corresponding triol; and then the triol is esterified with an esterifying species to form a triester species, wherein the esterifying species is selected from the group consisting of carboxylic acids, acyl halides, acyl anhydrides, and combinations thereof, and wherein the esterifying species has a carbon number of from 2 to 19. The structure of the triester prepared by the foregoing method would be as follows:

wherein R₂, R₃, and R₄ are typically the same or independently selected from C₂ to C₂₀ hydrocarbon groups, and are more typically selected from C₄ to C₁₂ hydrocarbon groups.

In another embodiment, the method can comprise reducing a monosaturated fatty acid to the corresponding unsaturated alcohol; epoxidizing the unsaturated alcohol to an epoxy fatty alcohol; and esterifying the fatty alcohol epoxide with an esterifying species to form a triester species, wherein the esterifying species is selected from the group consisting of carboxylic acids, acyl halides, acyl anhydrides, and combinations thereof, and wherein the esterifying species has a carbon number of from 2 to 19.

In some embodiments, where a quantity of such triester species is formed, the quantity of triester species can be substantially homogeneous, or it can be a mixture of two or more different such triester species. Additionally or alternatively, in some embodiments, such methods further comprise a step of blending the triester composition(s) with one or more diester species.

In some embodiments, such methods produce compositions comprising at least one triester species of the type 9,10-bis-alkanoyloxy-octadecanoic acid alkyl ester and isomers and mixtures thereof where the alkyl is selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, and octadecyl; and where the alkanoyloxy is selected from the group consisting of ethanoyloxy, propanoyoxy, butanoyloxy, pentanoyloxy, hexanoyloxy, heptanoyloxy, octanoyloxy, nonaoyloxy, decanoyloxy, undacanoyloxy, dodecanoyloxy, tridecanoyloxy, tetradecanoyloxy, pentadecanoyloxy, hexadeconoyloxy, and octadecanoyloxy. Exemplary such triesters include, but not limited to, 9,10-bis-hexanoyloxy-octadecanoic acid hexyl ester; 9,10-bis-octanoyloxy-octadecanoic acid hexyl ester; 9,10-bis-decanoyloxy-octadecanoic acid hexyl ester; 9,10-bis-dodecanoyoxy-octadecanoic acid hexyl ester; 9,10-bis-hexanoyloxy-octadecanoic acid decyl ester; 9,10-bis-decanoyloxy-octadecanoic acid decyl ester; 9,10-bis-octanoyloxy-octadecanoic acid decyl ester; 9,10-bis-dodecanoyloxy-octadecanoic acid decyl ester; 9,10-bis-hexanoyloxy-octadecanoic acid octyl ester; 9,10-bis-octanoyloxy-octadecanoic acid octyl ester: 9,10-bis-decanoyloxy-octadecanoic acid octyl ester; 9,10-bis-dodecanoyloxy-octadecanoic acid octyl ester; 9,10-bis-hexanoyloxy-octadecanoic acid dodecyl ester; 9,10-bis-octanoyloxy-octadecanoic acid dodecyl ester; 9,10-bis-decanoyloxy-octadecanoic acid dodecyl ester; 9,10-bis-doclecanoyloxy-octadecanoic acid dodecyl ester; and mixtures thereof.

In some such above-described method embodiments, the mono-unsaturated fatty acid can be a bio-derived fatty acid. In some or other such above-described method embodiments, the alcohol(s) can be FT-produced alcohols.

In some such above-described method embodiments, the step of esterifying (i.e., esterification) the mono-unsaturated fatty acid can proceed via an acid-catalyzed reaction with an alcohol using, e.g., H₂SO₄ as a catalyst. In some or other embodiments, the esterifying can proceed through a conversion of the fatty acid(s) to an acyl halide (chloride, bromide, or iodide) or acyl anhydride, followed by reaction with an alcohol.

Regarding the step of epoxidizing (i.e., the epoxidation step), in some embodiments, the above-described mono-unsaturated ester can be reacted with a peroxide (e.g., H₂O₂) or a peroxy acid (e.g., peroxyacetic acid) to generate an epoxy-ester species. See, e.g., D. Swern, in Organic Peroxides Vol. II, Wiley-Interscience, New York, 1971, pp. 355-533; and B. Plesnicar, in Oxidation in Organic Chemistry, Part C, W. Trahanovsky (ed.), Academic Press, New York 1978, pp. 221-253. Additionally or alternatively, the olefinic portion of the mono-unsaturated ester can be efficiently transformed to the corresponding dihydroxy ester by highly selective reagents such as osmium tetra-oxide (M. Schroder, Chem. Rev. vol. 80, p. 187, 1980) and potassium permanganate (Sheldon and Kochi, in Metal-Catalyzed Oxidation of Organic Compounds, pp. 162-171 and 294-296, Academic Press, New York, 1981).

Regarding the step of epoxide ring opening to the corresponding dihydroxy-ester, this step is usually an acid-catalyzed hydrolysis. Exemplary acid catalysts include, but are not limited to, mineral-based Brønsted acids (e.g., HCl, H₂SO₄, H₃PO₄, perhalogenates, etc.), Lewis acids (e.g., TiCl₄ and AlCl₃), solid acids such as acidic aluminas and silicas or their mixtures, and the like. See, e.g., Chem. Rev. vol. 59, p. 737, 1959; and Angew. Chem. Int. Ed., vol. 31, p. 1179, 1992. The epoxide ring opening to the diol can also be accomplished by base-catalyzed hydrolysis using aqueous solutions of KOH or NaOH.

Regarding the step of esterifying the dihydroxy-ester to form a triester, an acid is typically used to catalyze the reaction between the —OH groups of the diol and the carboxylic acid(s). Suitable acids include, but are not limited to, sulfuric acid (Munch-Peterson, Org. Synth., V, p. 762, 1973), sulfonic acid (Allen and Sprangler, Org. Synth., III, p. 203, 1955), hydrochloric acid (Eliel et al., Org. Synth., IV, p. 169, 1963), and phosphoric acid (among others). In some embodiments, the carboxylic acid used in this step is first converted to an acyl chloride (or another acyl halide) via, e.g., thionyl chloride or PCl3. Alternatively, an acyl chloride (or other acyl halide) could be employed directly. Where an acyl chloride is used, an acid catalyst is not needed and a base such as pyridine, 4-dimethylaminopyridine (DMAP) or triethylamine (TEA) is typically added to react with an HCl produced. When pyridine or DMAP is used, it is believed that these amines also act as a catalyst by forming a more reactive acylating intermediate. See, e.g., Fersh et al., J. Am. Chem. Soc., vol. 92, pp. 5432-5442, 1970; and Hofle et al., Angew. Chem. Int. Ed. Engl., vol. 17, p. 569, 1978. Additionally or alternatively, the carboxylic acid could be converted into an acyl anhydride and/or such species could be employed directly.

Regardless of the source of the mono-unsaturated fatty acid, in some embodiments, the carboxylic acids (or their acyl derivatives) used in the above-described methods are derived from biomass. In some such embodiments, this involves the extraction of some oil (e.g., triglyceride) component from the biomass and hydrolysis of the triglycerides of which the oil component is comprised so as to form free carboxylic acids.

In some particular embodiments, wherein the above-described method uses oleic acid for the mono-unsaturated fatty acid, the resulting triester is of the type:

wherein R₂, R₃ and R₄ are typically the same or independently selected from C₂ to C₂₀ hydrocarbon groups, and are more typically selected from C₄ to C₁₂ hydrocarbon groups.

Using a synthetic strategy in accordance with that outlined above, oleic acid can be converted to triester derivatives (9,10-bis-hexanoyloxy-octadecanoic acid hexyl ester) and (9,10-bis-decanoyloxy-octadecanoic acid decyl ester). Oleic acid is first esterified to yield a mono-unsaturated ester. The mono-unsaturated ester is subjected to an epoxidation agent to give an epoxy-ester species, which undergoes ring-opening to yield a dihydroxy ester, which can then be reacted with an acyl chloride to yield a triester product.

The strategy of the above-described synthesis utilizes the double bond functionality in oleic acid by converting it to the diol via double bond epoxidation followed by epoxide ring opening. Accordingly, the synthesis begins by converting oleic acid to the appropriate alkyl oleate followed by epoxidation and epoxide ring opening to the corresponding diol derivative (dihydroxy ester).

Variations (i.e., alternate embodiments) on the above-described processes include, but are not limited to, utilizing mixtures of isomeric olefins and or mixtures of olefins having a different number of carbons. This leads to diester mixtures and triester mixtures in the ester component.

Variations on the above-described processes include, but are not limited to, using carboxylic acids derived from FT alcohols by oxidation.

The present turbine oils, comprised of the base oil and ester component, show excellent properties as a lubricating oil for turbines. One of the most important characteristics is reduced sludge. The turbine oil composition will generally have less than 6 mg of sludge/100 ml of turbine oil as determined by the Cincinnati Milacron Thermal A Test. In some embodiments, the turbine oil exhibits less than 3 mg of sludge/100 ml of turbine oil. This overcomes a major problem which has been observed with regard to insoluble formation in turbine oils. By combining the present synthetic ester component, comprised of at least one diester or triester species having ester links on adjacent carbons, with a Group II, III and/or IV base oil, the present turbine oil exhibiting reduced sludge can be obtained.

In another embodiment, the turbine oil also contains an additive component. Antioxidants are additives which can be successfully used, which are known to the industry. In some embodiments, the antioxidant comprises at least one antioxidant other than a phenolic antioxidant, e.g., an amine antioxidant. Mixtures of antioxidants can be used, e.g., a mixture of aminic and phenolic antioxidants or a mixture of dithiocarbamate, tolutriazole and phenolic antioxidants. It has been found that favorable results are achieved when antioxidants other than phenolic antioxidants are used, whether in the absence of a phenolic antioxidant or in mixture with a phenolic antioxidant.

Other additive components which can be used in the present turbine oil for their respective functions include detergents, anti-wear agents, metal deactivators, corrosion inhibitors, rust inhibitors, friction modifiers, anti-foaming agents, viscosity index improvers, demulsifying agents, emulsifying agents, antioxidants, complexing agents, extreme pressure additives, pour point depressants, and combinations thereof.

In addition to reduced sludge, in some embodiments, the present turbine oils exhibit improved copper appearance, as measured by ASTM D130-10, and improved oxidation stability in RPVOT. The copper appearance indicates minimal copper corrosion, generally better than 3 A as determined by ASTM D130-10. The RPVOT oxidative stability, as measured by ASTM D22272-11, is at least 250 minutes, and in some embodiments is over 1000 minutes.

The combination of the base oil, ester component and any additives can be achieved by any suitable mixing means. Generally, the final turbine oil is comprised of from 0.5 to 15 wt % of the ester component and has a VI of at least 90.

The following examples are provided to demonstrate, and/or more fully illustrate, particular embodiments of the present invention. It should be appreciated by those of skill in the art that the methods disclosed in the examples which follow merely represent exemplary embodiments of the present invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments described and still obtain a like or similar result without departing from the spirit and scope of the present invention.

Example 1 Synthesis of a diol from Tetradecene

In a 3-neck 3-liter reaction flask equipped with an overhead stirrer and placed in an ice bath, 260 grams of 30% hydrogen peroxide (2.3 mol. H₂O₂) was added to 650 grams of 88 wt % formic acid (12.4 mol). To this mixture, 392 grams (2 mol.) of a mixture of tetradecene isomers (1-tetradecene, 2-tetradecene, 3-tetradecece, 4-tetradecene, 5-tetradecene, 6-tetradecene and 7-tetradecene) was added drop-wise via an addition funnel over a 45-minute period while keeping the reaction temperature below 45° C. Once the addition of the olefins was complete, the reaction was allowed to stir while cooling in an ice bath to prevent a rise in the temperature above 40-45° C., for 2 hrs. The ice bath was then removed and the reaction was allowed to stir at room temperature overnight. The reaction mixture was concentrated with a rotary evaporator in a hot water bath at about 30 mmHg to remove most of the water and formic acid. Then, 400 ml of ice-cold 1M solution of sodium hydroxide was added in small portions and carefully to the remaining reaction concentrate. Once all the sodium hydroxide solution was added, the mixture was allowed to stir for an additional 2 hours at about 75-80° C. The mixture was then diluted with 500 ml ethyl acetate and transferred to a separatory funnel. The organic layer was separated and the aqueous layer was extracted 3 times with ethyl acetate (300 ml each). The ethyl acetate extracts were all combined and dried over anhydrous MgSO₄. Filtration, followed by concentration on a rotary evaporator at reduced pressure in a hot water bath yielded a tetradecenes-diol mixture as a waxy substance in 96% yield (443 grams). The tetradecenes-diols were characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopes, as well as gas-chromatography/mass spectrometry (GC/MS).

Example 2 Synthesis of the Diester

In a 3-neck 1 L reaction flask equipped with an overhead stirrer, reflux condenser, and a dropping funnel, 440 grams (0.95 mol) of the tetradecenes-diol mixture (prepared as described above in Example 1), 1148 grams (5.7 mol) lauric acid, and 17.5 grams of 85 wt % H₃PO₄ (0.15 mol) were all mixed together. The resulting mixture was heated to 150° C. and stirred for several hours while monitoring the progress of the reaction by NMR spectral and GC/MS analysis. After stirring for 6 hours, the reaction was complete and the mixture cooled down to room temperature. The reaction mixture was washed with 1000 ml water and the organic layer was separated using a separatory funnel. The organic layer was further rinsed with brine solution (1000 ml of saturated sodium chloride solution). The resulting mixture was then distilled at 220° C. and 100 mmHg (Torr) to remove excess lauric acid. The diester product (the remaining residue in the distillation flask) was recovered as faint clear yellow oil in 84% yield (1000 grams). The mixture of diesters' product was hydrogenated to remove any residual olefins that could have formed by elimination during the esterification reaction. The final product, a colorless oil, was analyzed by IR and NMR spectroscopes, and by GC/MS.

The reactions and molecular transformation sequence is

for the epoxidation of 7-tetradecene, which is typical for all epoxidation and dihydroxylation of all other olefins via this method.

Example 3 Comparative Runs

Turbine oils were prepared by combining 5 wt % of the foregoing prepared diester of Example 2 with three different commercial Group II turbine oils: Turbine Oil-1; Turbine Oil-2; and Turbine Oil-3, which is an amine free version of Turbine Oil-2. The basic turbine oils already contained any additives, e.g., antioxidants. The physical characteristics and properties of the prepared turbine oils were then tested. The basic turbine oils, without the diester component, were also tested. The results are shown in Table 2 below. The amounts of the components of each Turbine Oil are noted in Table 2 in wt % of the overall turbine formulation.

TABLE 2 TURBINE OIL-1 TURBINE OIL-2 TURBINE OIL-3 EXP# 1 2 3 4 5 6 COMP. Asian Group II Oil 150 x x X x x x (hydrotreated API grp II basestock) Asian Group II Oil 600 x x X x x x (hydrotreated API group II basestock) Diesters (bio-derived 5 5 5 diester) wt % Additive package 1 1 comprising aminic and phenolic antioxidants and low acidity corrosion inhibitor Succinic acid corrosion 0.02 0.02 0.02 0.02 inhibitor Acrylic Foam inhibitor 0.0625 0.0625 0.05 0.05 Additive package 1 1 comprising phenolic and dithiocarbamate antioxidants, and low acidity corrosion inhibitor Pour point depressant 0.1 0.1 Polyacrylate foam 0.0075 0.0075 inhibitor Phenolic antioxidant 0.5 0.5 Low-acidity corrosion 0.12 0.12 inhibitor Viscosity at 40 C., cSt 33.40 32.13 33.23 31.98 33.27 32.01 Viscosity at 100 C., cSt 5.713 5.526 5.697 5.511 5.702 5.51 TESTING: Cincinnati Milacron Thermal A Copper Wt. Change, mg 0.9000 1.000 2.300 .300 2.000 1.800 Copper, Appearance, 1B 3A 2E 2E 3A 2E (ASTM D130) Sludge/100 ml oil, mg 1.95 7.75 5.10 6.50 6.50 3.55 Vis change at 40 C., % 0.51 .34 2.59 2.25 1.62 1.75 D974-Tan; Start 0.19 0.07 0.23 0.10 0.22 0.10 MGKOH/g D974-Tan; END 0.07 0.03 0.07 0.04 0.06 0.06 MGKOH/g rust 24 h 665B Pass/Pass Pass/Pass Pass/Pass Pass/Pass Pass/Pass Pass/Pass RPVOT (2272) 1666 1738 1120 1660 483 466

From the foregoing results, it can be seen that the present turbine oils containing the ester component can exhibit excellent and improved reduced sludge deposits. Note in particular the results of the Turbine Oil-1 and Turbine Oil-2. Improved copper appearance and oxidative stability can also be realized. Overall, an improved turbine oil is achieved by utilizing the ester component, which also offers an option of biodegradable turbine oils having reduced sludge.

All patents and publications referenced herein are hereby incorporated by reference to the extent not inconsistent herewith. It will be understood that certain of the above-described structures, functions, and operations of the above-described embodiments are not necessary to practice the present invention and are included in the description simply for completeness of an exemplary embodiment or embodiments. In addition, it will be understood that specific structures, functions, and operations set forth in the above-described referenced patents and publications can be practiced in conjunction with the present invention, but they are not essential to its practice. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without actually departing from the spirit and scope of the present invention as defined by the appended claims. 

1. A turbine oil comprised of a base oil selected from the group consisting of Group II, III, IV base oils and mixtures thereof, and an ester component comprised of at least one diester or triester species having ester links on adjacent carbons, with the turbine oil having less than 6 mg of sludge/100 ml of turbine oil as determined by Cincinnati Milacron Thermal A test.
 2. The turbine oil of claim 1, wherein the turbine oil has less than 3 mg of sludge/100 ml of turbine oil.
 3. The turbine oil of claim 1, further comprising at least one antioxidant other than a phenolic antioxidant.
 4. The turbine oil of claim 3, wherein the antioxidant comprises an amine antioxidant.
 5. The turbine oil of claim 3, wherein the antioxidant comprises a mixture of aminic and phenolic antioxidants.
 6. The turbine oil of claim 3, wherein the antioxidant comprises a mixture of dithiocarbamate, tolutriazole and phenolic antioxidants.
 7. The turbine oil of claim 1, wherein the base oil is a GTL base oil.
 8. The turbine oil of claim 1, wherein the base oil comprises less than 5 wt % aromatics.
 9. The turbine oil of claim 1, wherein the turbine oil comprises from 0.5 to 15 wt % of the ester component.
 10. The turbine oil of claim 9, wherein the turbine oil comprises from 5 to 10 wt % of the ester component.
 11. The turbine oil of claim 1, wherein the turbine oil comprises at least one other additive component selected from the group consisting of detergents, anti-wear agents, metal deactivators, corrosion inhibitors, rust inhibitors, friction modifiers, anti-foaming agents, viscosity index improvers, demulsifying agents, emulsifying agents, antioxidants, complexing agents, extreme pressure additives, pour point depressants, and combinations thereof.
 12. The turbine oil of claim 1, wherein the turbine oil has VI of at least 90, and having an RPVOT oxidative stability of from at least 250 minutes.
 13. The turbine oil of claim 1, wherein the ester component comprises a diester species having the following structure:

wherein R₁, R₂, R₃ and R₄ are identical or independently selected from hydrocarbon groups having from 2 to 17 carbon atoms.
 14. The turbine oil of claim 1, wherein the ester component comprises a diester species derived from a process comprising: a) epoxidizing an olefin having from about 8 to about 16 carbon atoms to form an epoxide comprising an epoxide ring; b) opening the epoxide ring of step a) and forming a diol; c) esterifying the diol of step b) with an esterifying species to form a diester species, wherein the esterifying species is selected from the group consisting of carboxylic acids, acyl halides, acyl anhydrides, and combinations thereof, wherein the esterifying species has a carbon number of from 2 to
 18. 15. The turbine oil of claim 1, wherein the ester component comprises a diester species derived from a process comprising: a) epoxidizing an olefin having from about 8 to about 16 carbon atoms to form an epoxide comprising an epoxide ring; and b) reacting the epoxide comprising the epoxide ring with an esterifying species to form a diester species, wherein the esterifying species is selected from the group consisting of carboxylic acids, acyl halides, acyl anhydrides, and combinations thereof, wherein the esterifying species has a carbon number of from 2 to
 18. 16. The turbine oil of claim 1, wherein the ester component comprises a triester species having the following structure:

wherein R₁, R₂, R₃ and R₄ are identical or independently selected from hydrocarbon groups having from 2 to 20 carbon atoms and wherein “n” is an integer from 2 to
 20. 17. The turbine oil of claim 1, wherein the ester component comprises a triester species having the following structure:

wherein R₂, R₃, and R₄ are identical or independently selected from C₂ to C₂₀ hydrocarbon groups.
 18. The turbine oil of claim 1, wherein the ester component comprises a triester species derived from a process comprising: a) esterifying a mono-unsaturated fatty acid having from 10 to 22 carbon atoms with an alcohol thereby forming an unsaturated ester; b) epoxidizing the unsaturated ester in step a) thereby forming an epoxy-ester species comprising an epoxide ring; c) opening the ring of the epoxy-ester species in step b) thereby forming a dihydroxy ester; and d) esterifying the dihydroxy ester in step c) with an esterifying species to form a triester species, wherein the esterifying species is selected from the group consisting of carboxylic acids, acyl halides, acyl anhydrides, and combinations thereof, and wherein the esterifying species has a carbon number of from 2 to
 19. 19. The turbine oil of claim 1, wherein the ester component comprises a triester species derived from a process comprising: a) reducing a monosaturated fatty acid to a corresponding unsaturated alcohol; b) epoxidizing the unsaturated alcohol to an epoxy fatty alcohol; c) opening a ring of the epoxy fatty alcohol to make a corresponding triol; and d) esterifying the triol of step c) with an esterifying species to form a triester species, wherein the esterifying species is selected from the group consisting of carboxylic acids, acyl halides, acyl anhydrides, and combinations thereof, and wherein the esterifying species has a carbon number of from 2 to
 19. 20. The turbine oil of claim 1, wherein the ester component comprises a triester species derived from a process comprising: a) reducing a monosaturated fatty acid to a corresponding unsaturated alcohol; b) epoxidizing the unsaturated alcohol to form a fatty alcohol epoxide; and c) esterifying the fatty alcohol epoxide with an esterifying species to form a triester species, wherein the esterifying species is selected from the group consisting of carboxylic acids, acyl halides, acyl anhydrides, and combinations thereof, and wherein the esterifying species has a carbon number of from 2 to
 19. 21. The turbine oil of claim 1, wherein the ester component is prepared using an esterifying species which is a carboxylic acid.
 22. The turbine oil of claim 21, wherein the carboxylic acid is derived from a bio-derived fatty acid.
 23. The turbine oil of claim 21, wherein the carboxylic acid is derived from alcohols generated by a Fischer-Tropsch process.
 24. The turbine oil of claim 1, having copper corrosion better than 3 A as determined by ASTM D130-10. 